The present invention relates to the design and construction of electrically energized valves employed for controlling flow of gaseous fuel to a burner. In particular, the present invention relates to gas fuel valves of the type employing a thermally actuated bi-metal element which deforms in response to electrical heating for opening the valve to permit flow of gaseous fuel to the burner.
It is known in the art to provide a thermally actuated gaseous fuel valve with a cantilever bi-metal arm having an elastomeric poppet provided on the free end thereof for movement between a closed position contacting a valve seat and a position spaced from the valve seat for permitting gaseous fuel flow over the valve seat to the valve outlet. Furthermore, it is known to employ an electrical resistance heating element disposed about the anchored end of the bi-metal arm for heating the arm in response to flow of electrical current through the resistance element. It is also known to configure the bi-metal arm in such a manner that in the unheated or unactuated condition, the bi-metal arm provides a preload biasing force to urge the resilient elastomeric poppet into contact with the valve seat.
In the aforesaid known thermally actuated gas valve construction, where a preload is provided for the poppet against the seat, the bi-metal arm must be heated to cause a predetermined amount of movement of the end thereof to release the preload on the poppet and effect poppet movement from the seat.
In such known thermally actuated gaseous fuel valves, the preload of the bi-metal arm against the poppet is absorbed by resilient deformation of the poppet in the portion thereof contacted by the free end of the bi-metal arm. Prior thermally actuated gaseous fuel valves have been calibrated such that the valve opens upon the flow of a predetermined current in the electrical heater actuator.
It has thus been the practice in known thermally actuated gaseous fuel valves to calibrate the opening or lifting of the poppet from the valve seat by deflection-preloading the bi-metal arm an amount equal to the movement thereof effected by the flow of the predetermined current. However, if the poppet does not provide elastic return of the local deformation under the preload of the bi-metal arm, the poppet may be caused to move from its seat at the onset of movement of the bi-metal arm under thermal actuation. This condition has occurred where the elastomeric material of the poppet has become "tacky" or where the elastomeric material has deformed around portions of the arm to prevent elastic return of the material upon initial movement of the bi-metal arm. This has thus caused the poppet to be lifted from the valve seat prematurely at an electrical current flow less than the calibrated level.
In certain types of fuel burner ignition control systems, the electrical thermally operated gaseous fuel valve is electrically connected with the control system such that the burner ignitor is activated by the flow of a predetermined current in the electrical actuator of the thermal valve. Thus, in such gaseous fuel burner ignition control systems, the condition of premature lifting of the valve poppet from the seat has resulted in the valve opening and discharge of fuel to the burner substantially in advance of the actuation of the burner ignitor. Therefore, it is vital that the poppet of an electrically actuated thermal gaseous fuel valve lift from its seat at the appropriate rated current flow to the electrical valve actuator.
Thus, it has been desired to find a way of preventing "sticking" of the elastomeric poppet and an electric thermally actuated gaseous fuel valve such that premature lifting of the poppet from its valve seat does not occur.